Assessment of Wind Damage to Commercial Roofing

In the wake of a Hurricane the monumental task of beginning to assess the losses and respond to the thousands of claims inevitably includes a number of claims concerning the functional assessment of commercial roofing systems. The design and construction of a roof system requires input from several disciplines including thermal considerations (Mechanical), fire resistance (Architect/Municipality), equipment carrying capacity (Structural), ability to drain and/or to store water (Architect/Civil), aesthetics, and the ability to resist any number of transient loads (Structural). The assessment of the damage sustained by a roof system during a storm event is an equally broad endeavor requiring the expert to call on a number of disciplines.

When assessing wind related damage to a roofing system, the damage observed may often be present among several other construction, design, and maintenance issues. This convolution is the basis for discrepancies in scope of repairs and cost. It is at this point when a Forensic Roof Expert (FRE) is often assigned to try and sort out the storm related damage from the construction defects, design problems, and maintenance issues.

The assessment of a roof for storm related damage generally begins with a visual assessment by the FRE. This would start with a brief assessment of the interior upper floor of a building to look for signs of water infiltration such as discoloration or delamination of finish materials. Evidence of water infiltration including oxidation of return air grills, diffusers, or suspended ceiling grid may indicate an ongoing problem and not that of a one time, recent event. Similarly, when possible, the underside of the roof structure should be observed for oxidation, wood rot, organic growth, or other signs of long-term exposure to moisture.

Subsequent to the initial assessment the need may arise for destructive or non-destructive testing of the roof system or components for the delineation of the scope of repairs. At this point in the assessment the FRE may be tasked with the job of delineating the area of the roof membrane and insulation that need to be removed and, based on this area, determine if the roof is repairable or needs to be replaced. There are several methods for determining the relative moisture content of insulation including: Conductance, Infrared Thermography, Capacitance, Nuclear Moisture Detection, and Cores/Laboratory.

Looking for conditions that are not storm related but that could contribute to water infiltration or other loss of function of the roof system is also recommended. The possible defects between construction, maintenance, and design are too numerous to list here. However, the most common deficiencies can be thought of in the following categories: poor drainage, inadequate ventilation, poor construction methods, inadequate design, and that the roof system is simply at the end of its service life.

In addition to the assessment of storm related damage, a parallel thought process should be to determine if the damage observed is consistent with the intensity of the storm; should the roof have performed better. The evaluation of the performance of a roof system is difficult when the roof is near the end of its service life, drawings and specifications are not available, and when applicable code or reinforcement of the code is unknown. On newer roofs built under the enforcement of new requirements, the performance of the roof can be compared to weather data. If the performance of the system falls short of expected, further investigation by the FRE can shed light on the potential cause. For example, samples sent for laboratory analysis can determine the rate of inter-ply mopping of asphalt for comparison with specifications, membrane samples can be tested for tensile and seam strength, under deck observations can determine fastener type and patterns, uplift testing using a vacuum chamber can measure the deflection of a membrane at a specific uplift pressure, and opening portions of the system for observation can reveal fastener patterns, type, insulation type, condition of deck and adherence of components.

These additional tests and investigative techniques in the hands of someone who understands the design process of the roof and local code requirements can be compared to the construction documents and design intent of the system for determination of possible avenues for subrogation.

In summary, one of the most forgotten and neglected building systems happens to be one of the most complicated systems requiring design inputs from several disciplines and impacts the performance of equally as many systems after construction. The evaluation of the damage to and performance of the roof system requires an expert that can pull these several disciplines together for a global perspective of performance of the system.

David P. Amori, PE, RRC, Vice President of Engineering at EFI Global, is a Structural / Geotechnical Engineer and Registered Roof Consultant with more than 22 years of domestic and international experience in building and heavy civil construction and engineering. His responsibilities include the oversight of the engineering service line, product delivery, quality, training and mentoring, business development, and executive team liaison.